Ni–Cu based catalysts prepared by two different methods and their catalytic activity toward the ATR of methane

Catalytic Reactivity Assessment of AgM and CuM (M = Cr, Fe) Catalysts for Dry Reforming of Methane Process with CO2

CuM and AgM (M = Cr, Fe) catalysts were synthesized, characterized, and evaluated in methane reforming with CO2 with and without pretreatment under a H2 atmosphere. Their textural and structural characteristics were evaluated using various physicochemical methods, including XRD, B.E.T., SEM-EDS, XPS, and H2-TPR. It was shown that the nature of the species has a significant effect on these structural, textural, and reactivity properties. AgCr catalysts, presenting several oxidation states (Ag0, Ag+1, Cr3+, and Cr6+ in Ag, AgCrO2, and AgCr2O4), showed the most interesting catalytic performance in their composition. The intermediate Cr2O3 phase, formed during the catalytic reaction, played an important role as a catalytic precursor in the in situ production of highly dispersed nanoparticles, being less prone to coke formation in spite of the severe reaction conditions. In contrast, the AgFe catalyst showed low activity and a low selectivity for DRM in the explored temperature range, due to a significant contribution of the reverse water-gas shift reaction, which accounted for the low H2/CO ratios.

Mechanistic Insights for Dry Reforming of Methane on Cu/Ni Bimetallic Catalysts: DFT-Assisted Microkinetic Analysis for Coke Resistance

Density functional theory (DFT) calculations have been utilized to evaluate the complete reaction mechanism of methane dry reforming (DRM) over Ni2Cu (111) bimetallic catalyst. The detailed catalytic cycle on Ni2Cu (111) catalyst demonstrated superior coke resistance compared to pure Ni (111) and Ni2Fe (111) reported in the literature. Doping Cu in the Ni–Ni network enhanced the competitive CH oxidation by both atomic O and OH species with the latter having only 0.02 eV higher than the 1.06 eV energy barrier required for CH oxidation by atomic O. Among the C/CH oxidation pathways, C* + O* → CO (g) was the most favorable with an energy barrier of 0.72 eV. This was almost half of the energy barrier required for the rate-limiting step of CH decomposition (1.40 eV) and indicated enhanced coke deposition removal. Finally, we investigated the effect of temperature (800~1000 K) on the carbon deposition and elimination mechanism over Ni2Cu (111) catalyst. Under those realistic DRM conditions, the calculations showed a periodic cycle of simultaneous carbon deposition and elimination resulting in improved catalyst stability.

Lanthanum Ferrites-Based Exsolved Perovskites as Fuel-Flexible Anode for Solid Oxide Fuel Cells

Exsolved perovskites can be obtained from lanthanum ferrites, such as La_0.6Sr_0.4Fe_0.8Co_0.2O₃, as result of Ni doping and thermal treatments. Ni can be simply added to the perovskite by an incipient wetness method. Thermal treatments that favor the exsolution process include calcination in air (e.g., 500 °C) and subsequent reduction in diluted H₂ at 800 °C. These processes allow producing a two-phase material consisting of a Ruddlesden–Popper-type structure and a solid oxide solution e.g., α-Fe_100-y-zCo_yNi_zO_x oxide. The formed electrocatalyst shows sufficient electronic conductivity under reducing environment at the Solid Oxide Fuel Cell (SOFC) anode. Outstanding catalytic properties are observed for the direct oxidation of dry fuels in SOFCs, including H₂, methane, syngas, methanol, glycerol, and propane. This anode electrocatalyst can be combined with a full density electrolyte based on Gadolinia-doped ceria or with La_0.8Sr_0.2Ga_0.8Mg_0.2O₃ (LSGM) or BaCe_0.9Y_0.1O_3-δ (BYCO) to form a complete perovskite structure-based cell. Moreover, the exsolved perovskite can be used as a coating layer or catalytic pre-layer of a conventional Ni-YSZ anode. Beside the excellent catalytic activity, this material also shows proper durability and tolerance to sulfur poisoning. Research challenges and future directions are discussed. A new approach combining an exsolved perovskite and an NiCu alloy to further enhance the fuel flexibility of the composite catalyst is also considered. In this review, the preparation methods, physicochemical characteristics, and surface properties of exsoluted fine nanoparticles encapsulated on the metal-depleted perovskite, electrochemical properties for the direct oxidation of dry fuels, and related electrooxidation mechanisms are examined and discussed.

Catalysis effect on CO2 methanation using MgH2 as a portable hydrogen medium

The feasibility of the reduction of CO2 to CH4 employing MgH2 in the presence and absence of cobalt as a catalyst was investigated for the first time, exploring different non-independent reaction conditions such as the grade of microstructural refinement, the molar ratio MgH2 : CO2, reaction time and temperature. For the un-catalyzed process a methane yield of 44.6% was obtained after 24 h of thermal treatment at 400 °C employing a molar ratio of 2 : 1, through a methanation mechanism that involves the direct reduction of CO2 and the generation of CH4via C as an intermediary. For the MgH2 catalyzed process a methane yield of 78% was achieved by heating at 350 °C for 48 h, 4 : 1 being the optimal molar ratio. The global mechanism corresponds to a Sabatier process favored by Co as an active catalyst, together with the reverse water gas shift reaction followed by methanation of CO in the presence of steam. On account of the fact that it was proved that the use of the catalyst allows lowering the operational temperature without collapsing the methane yield, this research provides interesting insight into a thermochemical method for CO2 reduction to CH4 employing a solid hydrogen storage medium as an H2 source.

Recent Progresses in Constructing the Highly Efficient Ni Based Catalysts With Advanced Low-Temperature Activity Toward CO2 Methanation

With the development and prosperity of the global economy, the emission of carbon dioxide (CO2) has become an increasing concern. Its greenhouse effect will cause serious environmental problems, such as the global warming and climate change. Therefore, the worldwide scientists have devoted great efforts to control CO2 emissions through various strategies, such as capture, resource utilization, sequestration, etc. Among these, the catalytic conversion of CO2 to methane is considered as one of the most efficient routes for resource utilization of CO2 owing to the mild reaction conditions and simple reaction device. Pioneer thermodynamic studies have revealed that low reaction temperature is beneficial to the high catalytic activity and CH4 selectivity. However, the low temperature will be adverse to the enhancement of the reaction rate due to kinetic barrier for the activation of CO2. Therefore, the invention of highly efficient catalysts with promising low temperature activities toward CO2 methanation reaction is the key solution. The Ni based catalysts have been widely investigated as the catalysts toward CO2 methanation due to their low cost and excellent catalytic performances. However, the Ni based catalysts usually perform poor low-temperature activities and stabilities. Therefore, the development of highly efficient Ni based catalysts with excellent low-temperature catalytic performances has become the research focus as well as challenge in this field. Therefore, we summarized the recent research progresses of constructing highly efficient Ni based catalysts toward CO2 methanation in this review. Specifically, the strategies on how to enhance the catalytic performances of the Ni based catalysts have been carefully reviewed, which include various influencing factors, such as catalytic supports, catalytic auxiliaries and dopants, the fabrication methods, reaction conditions, etc. Finally, the future development trend of the Ni based catalysts is also prospected, which will be helpful to the design and fabrication of the Ni catalysts with high efficiency toward CO2 methanation process.

Investigation of NiFe-Based Catalysts for Oxygen Evolution in Anion-Exchange Membrane Electrolysis

NiFe electrodes are developed for the oxygen evolution reaction (OER) in an alkaline electrolyser based on an anion exchange membrane (AEM) separator and fed with diluted KOH solution as supporting electrolyte. This study reports on the electrochemical behaviour of two different NiFe-oxide compositions (i.e., Ni1Fe1-oxide and Ni1Fe2-oxide) prepared by the oxalate method. These catalysts are assessed for single-cell operation in an MEA including a Sustainion™ anion-exchange membrane. The electrochemical polarization shows a current density of 650 mA cm−2 at 2 V and 50 °C for the Ni1Fe1 anode composition. A durability test of 500 h is carried out using potential cycling as an accelerated stress-test. This shows a decrease in current density of 150 mA cm−2 mainly during the first 400 h. The performance achieved for the anion-exchange membrane electrolyser single-cell based on the NiFeOx catalyst appears promising. However, further improvements are required to enhance the stability under these operating conditions.

Tuning Catalytic Properties of Supported Bimetallic Pd/Ir Systems in the Hydrogenation of Cinnamaldehyde by Using the “Water-in-Oil” Microemulsion Method

Supported Pd/Ir bimetallic catalysts were synthesized by the “water-in-oil” microemulsion method at different precursor concentrations and characterized by XRD, XPS, SEM, TEM, and cyclic voltammetry. Depending on the preparation conditions, formation of bimetallic catalysts with different metal segregation and surface composition can be easily obtained, thus tuning the bimetallic structure of catalysts as well as their relative catalytic properties. Bimetallic Pd/Ir systems were efficiently tested in the hydrogenation of cinnamaldehyde showing a better performance than analogous monometallic catalysts.

Core-Shell Sn-Ni-Cu-Alloy@Carbon Nanorods to Array as Three-Dimensional Anode by Nanoelectrodeposition for High-Performance Lithium Ion Batteries

We report the synthesis of a novel three-dimensional anode based on the core-shell Sn-Ni-Cu-alloy@carbon nanorods which was fabricated by pulse nanoelectrodeposition. Li ion batteries equipped with the three-dimensional anode demonstrated almost 100% capacity retention over 400 cycles at 450 mA g(-1) and excellent rate performance even up to 9000 mA g(-1) for advanced Li-ion battery. Insight of the high performance can be attributed to three key factors, Li-Sn alloys for Li-ion storage, Ni-Cu matrix for the electronic conductive and nanorods structure, and the carbon shell for the electronic/Li-ion conductive and holding stable solid electrolyte interphase (SEI), because these shells always kept stable volumes after extension of initial charge-discharge cycles.